heptapeptide is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-05-21. Where a claim depends on a specific study, the study is described rather than over-claimed.
Thymosin beta-4 is a 43-residue actin-binding protein found in most mammalian cell types, where it participates in cytoskeletal regulation and cell migration. TB-500 represents only a short fragment of that protein and does not include the remaining residues. Whether the isolated fragment reproduces the full range of activities reported for the intact protein remains an open question. Researchers commonly treat the two as related but distinct entities when comparing results.
Published work involving this sequence spans actin-binding assays, cell-migration studies, wound-healing models, and cardiovascular or musculoskeletal experiments. Much of the biological rationale derives from in vitro systems and animal models, and the number of controlled human studies is small. Reported outcomes vary across preparations, doses, and routes, which complicates comparison between studies. Reviews generally describe the evidence base as preliminary rather than settled. Mechanistic explanations are often proposed by analogy to the parent protein rather than demonstrated directly.
TB-500 is a research peptide whose sequence matches residues 17 to 23 of thymosin beta-4, a 43-residue protein present in most mammalian cells. The chain is seven amino acids long, written as LKKTETQ, and is normally supplied with an acetyl group on the N-terminus. Suppliers list it as a lyophilised powder under the code name TB-500, and the same sequence appears elsewhere in catalogues as the thymosin beta-4 actin-binding fragment. The label is commercial rather than systematic, so no single authority fixes exactly what TB-500 denotes.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Acetylated heptapeptide form |
| Monoisotopic mass | 888.5 Da | Average mass about 889 Da |
| Appearance | White to off-white solid | Usually supplied as lyophilised powder |
| Solubility class | Highly water soluble | Also dissolves in aqueous buffers |
| Common synonyms | Tbeta4 fragment, thymosin beta-4 (17-23) | Refer to the same sequence |
Peptide bonds are susceptible to hydrolysis under extreme pH and to enzymatic cleavage if proteases are present. Heat, oxidising agents, and prolonged exposure to light also contribute to loss of material. Aggregation can occur at high concentrations or in certain buffer systems, and it may not be visible to the eye. Storage at -20 C or below is typical for both powder and aliquoted solutions, and desiccation of the powder is preferred.
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography together with mass spectrometry. The chromatogram provides a purity estimate as a percentage of total peak area, while the mass spectrum confirms that the observed mass matches the expected value. Amino acid analysis or tandem mass spectrometry sequencing can provide additional confirmation. Reported purity figures depend on the column, gradient, and detection wavelength, so values from different laboratories are not directly comparable without method details.
Lyophilised peptide is normally reconstituted with sterile water or a neutral buffer shortly before use. Because repeated freeze-thaw cycles can degrade the material, dividing a reconstituted solution into single-use aliquots is a common practice. Working solutions are usually kept cold and protected from light. The exact shelf life depends on concentration, buffer composition, and handling, so it is often determined empirically rather than assumed.
Identity and purity are checked with reversed-phase high-performance liquid chromatography, which separates the target sequence from truncated or deletion analogues, and with mass spectrometry, which confirms the expected molecular mass. Amino acid analysis and peptide mapping give orthogonal confirmation but are used less often outside specialist laboratories. Counter-ion content varies: material purified on trifluoroacetic acid gradients retains trifluoroacetate, and ion exchange can convert the salt form. Residual water and solvent are measured by Karl Fischer titration or thermogravimetric analysis, and any purity figure should be read together with the method used to obtain it.
Lyophilised peptide powders are hygroscopic, and the fragment absorbs atmospheric moisture when a vial is opened at room temperature. Weighing and aliquoting are normally done quickly in a dry environment, and stock solutions are divided into single-use portions before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and can shift the measured content of a vial. These practices are general to synthetic peptides rather than unique to this sequence, but they matter more for short chains kept for long periods.
The seven-residue chain carries several polar and charged side chains, so it dissolves readily in water and in aqueous buffers near neutral pH. No cysteine is present, so disulphide formation is not a concern and reducing agents are unnecessary. Dilute ammonium hydroxide or acetonitrile-water mixtures are sometimes used for stock solutions when initial dissolution is slow. Strongly alkaline conditions and prolonged contact with oxidising agents are avoided because they can modify lysine-containing stretches, and haze in solution usually signals incomplete dissolution or aggregated material.
Proposed activity centers on actin sequestration and on the movement of cells during repair processes. In cell culture and animal models, the fragment has been associated with migration, tube formation, and tissue remodeling. These observations are frequently described as preliminary, because most published work uses rodent or in vitro systems rather than controlled human trials. Whether the short fragment reproduces the effects of the full protein remains an open question, and the relationship between dose, route, and measured outcome is not well characterized.
The compound circulates in the literature as a research reagent rather than an approved therapeutic. Regulatory agencies in several countries have not authorized it for medical use, and sporting bodies list related thymosin beta-4 peptides among prohibited substances. Suppliers typically market it with a purity figure and a certificate of analysis, while peer-reviewed clinical reports remain sparse. Discussions therefore often separate laboratory findings from anecdotal reports, and reviewers tend to note the small size and methodological limits of the available studies.
=== Fiction === Orlando Gardiner, one of the main characters in Tad Williams' science fiction tetralogy Otherland, suffers from progeria. Due to his illness, he spends a lot of time gaming on the net as Thargor, the barbarian. Over the course of the story, he dies at 14 years of age. The protagonist of the 2009 Hindi feature film Paa is a boy with a rare genetic condition progeria and the film focuses on his relationship with his parents. The episode "Scientific Method" of the television series Star Trek: Voyager features an adult character who experiences advanced aging after his genes are altered, leading the ship's doctor to draw a comparison with progeria. Kimberly Akimbo, both the 2021 Broadway Musical (Tony Award for Best Musical) and the 2001 play, tell the story of a 16-year-old girl with a progeria-like disease. Both the play and musical, book and lyrics, are by David Lindsay-Abaire, with Jeanine Tesori writing the music.
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=== Names === Etilefrine is the generic name of the drug and its INNTooltip International Nonproprietary Name and BANTooltip British Approved Name, while étiléfrine is its DCFTooltip Dénomination Commune Française and etilefrina is its DCITTooltip Denominazione Comune Italiana. In the case of the hydrochloride salt, its generic name is etilefrine hydrochloride and this is its BANMTooltip British Approved Name and JANTooltip Japanese Accepted Name. Synonyms of etilefrine include ethylnorphenylephrine, ethylphenephrine, etiladrianol, aethyladrianol, and M-I-36. Brand names of the drug include Effortil, Circupon, Apocretin, Palsamin, Kertasin, Pressoton, Effoless, and Sanlephrin.
Sources: en.wikipedia.org
=== 2 December === The commander of the SAF's 22nd Infantry Division, Major-General Abdelmajid al-Haj, and an unidentified brigadier general who commanded the SAF's 170th Artillery Brigade were killed in an RSF ambush while retreating from Babanusa towards Heglig. The SAF retook the town of Mabsouta in South Kordofan from the SPLM-N (al-Hilu), which had occupied the area since 2011.
== Predictive value == Murphy's sign has a high sensitivity and negative predictive value, although the specificity is not high. However, in the elderly the sensitivity is markedly lower; a negative Murphy's sign in an elderly person is not useful for ruling out cholecystitis if other tests and the clinical history suggest the diagnosis.
Triorganosilyl sources have quite variable prices, and the most economical is chlorotrimethylsilane (TMS-Cl), a Direct Process byproduct. The trimethylsilyl ethers are also extremely sensitive to acid hydrolysis (for example silica gel suffices as a proton donator) and are consequently rarely used nowadays as protecting groups.
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Sources: en.wikipedia.org
No. TB-500 is a short synthetic peptide matching residues 17 to 23 of thymosin beta-4, while the parent protein contains 43 residues. The fragment lacks the rest of the protein sequence, so the two are related but not identical.
It consists of leucine, lysine, lysine, threonine, glutamic acid, threonine, and glutamine in that order. The N-terminal leucine is usually acetylated in the forms described in catalogues.
Controlled human data is limited, and most published findings come from cell culture or animal work. This makes it difficult to state clinical effects with confidence.
No. Thymosin beta-4 is a 43-residue protein, while TB-500 matches only residues 17 to 23 of that chain. The two are related but differ in size, and a method that identifies one does not automatically identify the other.